The objectives of the IARC Monographs Programme on the Evaluation of Carcinogenic Risks to Humans are to critically review and evaluate the strength of the total published scientific evidence for carcinogenic risk from biological, physical, and chemical agents, complex mixtures, and exposure circumstances to which humans are exposed, and to publish these reviews and evaluations in book form as IARC Monographs. The long-term goal is to provide evaluations of all significant environmental contributing causes of human cancer, and to re-evaluate those for which evidence is incomplete at the time of initial evaluation whenever new findings provide additional evidence which may change a previous evaluation. A further goal for the immediate future that is to supplement the existing hard-copy publications by complete, searchable electronic versions that will be available both on-line by internet and as CD-ROM. The Preamble to the IARC Monographs defines the guiding principles for making evaluations of carcinogenicity on the basis of epidemiologic studies, bioassays for carcinogenicity in experimental animals, and other relevant data (e.g., toxicity, metabolism, genetic toxicology, and mechanisms of carcinogen action). Nominations for evaluations are solicited worldwide and prioritized and prioritized by ad-hoc international advisory groups of scientific and public health experts at intervals of approximately five years. The Programme sponsors scientific meetings on carcinogenic mechanisms and other subjects relevant to evaluations of carcinogenicity, and publishes (in electronic form on the Internet) a Directory of Agents being Tested for Carcinogenicity worldwide, to facilitate communication among scientists and to reduce unnecessary duplication of effort. Each volume of the IARC Monographs results from the deliberations of an international working group of 202-25 experts in cancer epidemiology, experimental carcinogenesis and related disciplines from 8-12 countries which meets in Lyon for one week; three meetings are held each year. The Monographs are of value to scientists and public health officials as authoritative summaries of the published literature; to regulatory authorities as one source of information on which to base risk assessments and risk management and risk management initiatives; and to private individuals as a reliable reference text.